The objective of the proposed research is to explore the role of collagenase in collagen breakdown and to learn how this breakdown is controlled by pharmacologic doses of steroid hormones. These studies will involve the involutind rat uterus, a system known to show the most rapid breakdown of collagen. Two important observations have recently been made on this system: collagenase can be assayed directly in uterine homogenates, and estradiol treatment inhibits collagen breakdown and reduces the level of assayable collagenase. It is proposed to isolate and purify collagenase directly from the uterus in order to compare it to collagenase from uterine cultures. Methods will be developed to assay the various forms of free and bound collagenase in the uterus. These methods will be used to see if collagenase activity is correlated with the rate of collagen breakdown during the postpartum involution of the uterus. The development of direct tissue assays will permit the evaluation of hormonal effects on collagenase in the intact animal, as opposed to current methods which are limited to culture techniques. Estradiol, progesterone and testosterone will be tested to see if their known effects on collagen breakdown are due to an inhibition of breakdown and if these effects are mediated by changes in collagenase activity.